Is there a way to register an AF point, keep it registered and then turn off the visual reminder in the viewfinder?
I don't belive so, unless you register it in 61pt. automatic selection AF mode, Pg. 338 of the manual. That's why I turned mine off, as it's quite distracting and annoying.
I have been manually moving around the AF points with the multi-controller and then one quick center press of the multi-controller returns me to the center AF point position.